The present invention relates to an apparatus for analyzing particles by passing a sample liquid containing particle components such as blood and urine in a sheath flow, irradiating light to the sample liquid flow, detecting the light from the particles, and analyzing the particles, and more particularly to an apparatus for analyzing particles capable of obtaining intense fluorescence without variance (dispersion) among particles, by irradiating the sample liquid flowing in a flat flow with a uniform and intense fluorescent excitation (excited) light. The sheath flow is a flow which covers the suspension of particles with a laminar sheath liquid in order to pass the particles by aligning them in one row precisely in the middle of the liquid flow. As the sheath liquid, usually, a diluent liquid or the like is used.
There is conventionally an apparatus for classifying and counting particles by irradiating particles with a fluorescent excitation light such as dyed cells, and detecting the fluorescence emitted from the particles. An example thereof is a flow cytometer. In the flow cytometer, in order to increase the number of particles to be analyzed, the sample liquid flow is passed in a broad (wide) flow in one direction, instead of a columnar flow. As disclosed in Published Japanese Laid-open Patent Sho. 57-500995 (which corresponds with U.S. Pat. No. 4,338,024), the sample flow containing particles is flattened to a flat flow, and still pictures of particles are taken by a strobe light and video camera.
In the flow cytometer, it is necessary to irradiate the flowing region of the sample liquid with a uniform light. When the sample liquid flow is a flat flow, as shown in FIG. 1, light 102 from a laser light source 100 is formed into an elliptical light by using cylinder lens or prism 104, and irradiating the sample flow 106 from the front (the broader side of the flat flow), so that the light intensity may be uniform.
However, the light intensity distribution emitted from the laser light source has a Gaussian distribution, and if, for example, an elliptical spot of 10.times.300 .mu.m is formed, the actual uniform range of light intensity is only 20 to 30 .mu.m in the central part thereof. Accordingly, if it is desired to have a uniform light intensity in a measuring region of about 150 .mu.m in width of a sample flat flow, the major diameter (axis) of the ellipse must be considerably longer, namely, several millimeters. When the major diameter of the ellipse is longer, the excitation light intensity per unit area becomes smaller, and the obtained fluorescence is feeble, and is hard to detect.
Besides, by irradiating the front of the flat flow by fluorescent excitation light, it is impossible to detect the side scattered light or side fluorescence from the side surface (the narrower side of the flat flow), and it is impossible to adjust the focus in the entire measuring region.
The art for making the irradiation light intensity uniform was disclosed in (a) Published Japanese Laid-open Patent Hei. 3-200051, and (b) Published Japanese Laid-open Patent Hei. 2-304333.
In (a), the irradiated light is reflected by a corner cube prism to form a plurality of parallel laser beam rows. The light is made uniform by overlapping parts of the incident light and reflected light. In (b), a light concentration (density) plate low in transmissivity in its middle portion and high on its sides is used to produce a uniform light intensity.
However, in (a), the light must be reflected continuously within the same plane, and it is difficult to adjust the prism position, which is not practical.
In (b), it is difficult to manufacture a light concentration plate having uniform characteristics, and it is also hard to adjust the position of the light concentration plate. Besides, the light is attenuated (damped).